Furnace Filters
Best 18x18 Furnace Filter (2026): Top 5 by the Specs
As an Amazon Associate I earn from qualifying purchases. Specs below come from each product's Amazon listing; we do not test products in person.
For an 18x18 furnace filter, the Simply 18x18x1 leads this list: it pairs MERV 8 pleated filtration with a 6-pack and an actual size of 17.75 by 17.75 by 0.75 inches. If you want a higher MERV rating, the Filtrete 18x18x1 offers MERV 11 and MPR 1000 in a 4-pack.
Starting out? See the main guide: Best Furnace Air Filters
Top picks at a glance
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Best OverallSimply 18x18x1 Air Filter9.8 View on Amazon -
Runner-UpFiltrete 18x18x1 Air Filter9.7 View on Amazon -
Also GreatAerostar Air Filter 18x18x1 MERV 8 AC9.5 View on Amazon -
Also GreatGlasfloss ZL 18x18x1 MERV 10 Air Filters9.4 View on Amazon -
Also GreatFlanders Air Filter E-Z Flow II9.2 View on Amazon
Compare the specs
Ranked on pack size from each listing, plus how many buyers have rated it. A dash (—) means we could not confirm that figure from the listing.
| Pick | MERV rating | Pack size | Weight | Warranty |
|---|---|---|---|---|
| 1. Simply 18x18x1 Air Filter | MERV 8 | 6-pack | — | — |
| 2. Filtrete 18x18x1 Air Filter | MERV 11 | 4-pack | — | — |
| 3. Aerostar Air Filter 18x18x1 MERV 8 AC | MERV 8 | 6-pack | — | — |
| 4. Glasfloss ZL 18x18x1 MERV 10 Air Filters | MERV 10 | 4-pack | — | — |
| 5. Flanders Air Filter E-Z Flow II | MERV 4 | — | — | — |
Simply 18x18x1 Air Filter
MERV 8 pleated filtration in a 6-pack at nominal 18x18x1, with an actual size of 17.75 by 17.75 by 0.75 inches.
- MERV rating: MERV 8
- Pack size: 6-pack
Good for
- Buyers with central units who want a 6-pack
- Buyers who want pleated filtration at MERV 8
Skip it if
- You need a MERV rating above MERV 8
- You need an actual depth above 0.75 inches
It has pleated media with a higher pleat count than most retail, trapping 90% of airborne particles, with airflow arrows for the filter slot. Filtration lasts up to 3 months, and the pack holds 6 filters. It is made in the USA from American components, including recycled materials.
Filtrete 18x18x1 Air Filter
MERV 11 and MPR 1000 pleated filtration in a 4-pack, with 3-month change intervals and app reminders.
- MERV rating: MERV 11
- Pack size: 4-pack
Good for
- Buyers who want MERV 11 and MPR 1000 filtration
- Buyers who want 30-, 60- or 90-day change reminders
Skip it if
- You need a MERV rating above MERV 11
- You want a pack larger than a 4-pack
It uses 3-in-1 technology to pull in and trap particles, and it captures microparticles 0.3 to 1.0 in size. Change it at least once every 90 days. The Filtrete Smart App sets 30-, 60- or 90-day reminders, and it carries a limited warranty.
Aerostar Air Filter 18x18x1 MERV 8 AC
MERV 8 pleated filtration in a 6-pack, with electrostatically charged media and a heavy-duty beverage board frame.
- MERV rating: MERV 8
- Pack size: 6-pack
Good for
- Buyers who want MERV 8 filtration at MPR 600
- Buyers with a standard 1-inch filter slot
Skip it if
- You need a MERV rating above MERV 8
- You want an actual depth above 0.75 inches
Electrostatically charged pleated media traps particles while allowing smooth air flow. The heavy-duty beverage board frame has moisture-resistant backing and reinforced pleats. Filtration lasts up to 3 months, and the pack holds 6 filters. It is made in the USA.
Glasfloss ZL 18x18x1 MERV 10 Air Filters
MERV 10 filtration in a 4-pack, with an exact size of 17-1/2 by 17-1/2 by 7/8 inches and a heavy-duty frame.
- MERV rating: MERV 10
- Pack size: 4-pack
Good for
- Buyers who want MERV 10 filtration
- Buyers who want a heavy-duty frame
Skip it if
- You need a MERV rating above MERV 10
- You want a pack larger than a 4-pack
Its MERV 10 rating compares to MPR 600 to 800 and FPR 5 to 6. It fits homes, businesses, schools, apartments, hotels and industrial applications. It is made in the USA.
Flanders Air Filter E-Z Flow II
MERV 4 flat panel filtration in a 12 pack, with spun fiberglass media and no metal media retainers.
- MERV rating: MERV 4
Good for
- Buyers who want basic MERV 4 filtration
- Buyers who want a 12 pack for frequent changes
Skip it if
- You need a MERV rating above MERV 4
- You want a change interval longer than 30 days
Spun fiberglass media captures dust and lint, and the flat panel fits standard 18 by 18 by 1 slots. Replacement is recommended every 30 days.
How to choose
Match nominal size to actual size
Nominal 18x18x1 filters measure smaller in practice. The Simply measures 17.75 by 17.75 by 0.75 inches, the Filtrete measures 17.68 by 17.68 by 0.81 inches, the Aerostar measures 17.50 by 17.50 by 0.75 inches, and the Glasfloss measures 17-1/2 by 17-1/2 by 7/8 inches. Check the slot depth against the actual size before ordering.
Read MERV, MPR and FPR together
MERV is the shared rating for particle capture, while MPR and FPR appear on some listings beside it. The Filtrete pairs MERV 11 with MPR 1000, the Aerostar pairs MERV 8 with MPR 600 and FPR 5, and the Glasfloss pairs MERV 10 with MPR 800 and FPR 7. Compare the same scale across picks, since each scale runs on its own numbers.
Change on a schedule
Change intervals differ: the Filtrete lists at least once every 90 days, the Simply and Aerostar list up to 3 months, and the Flanders lists every 30 days. The Filtrete Smart App sets 30-, 60- or 90-day reminders. Follow the airflow arrows when inserting a filter into the slot.
FAQ
What is the actual size of an 18x18x1 filter?
It varies by pick. The Simply measures 17.75 by 17.75 by 0.75 inches, the Filtrete measures 17.68 by 17.68 by 0.81 inches, and the Aerostar measures 17.50 by 17.50 by 0.75 inches.
When should I change an 18x18 furnace filter?
The Flanders lists every 30 days, the Filtrete lists at least once every 90 days, and the Simply and Aerostar list up to 3 months.
What does MERV mean on a furnace filter?
MERV rates particle capture for a filter. Picks here range from MERV 4 on the Flanders to MERV 11 on the Filtrete, with MERV 8 and MERV 10 between them.
